Development of alternatives to fossil fuels is a major scientific and economic concern. Such fuels have the potential to provide a reliable and sustainable source of energy, while at the same time greatly limiting release of carbon dioxide to the environment from the burning of fossil fuels. The term biofuel refers to a fuel that is biological in origin and is in some way derived from the biomass of a plant or other organic matter. Biofuels can be in solid, liquid, or gaseous form and can be used in a variety of ways, ranging from the combustion of wood for heating to the use of bioethanol and biodiesel as a transportation fuel. When considering liquid transportation fuels, multiple feedstocks have been studied and developed. In particular, ethanol derived from corn stands out as the most mature and widely commercialized option. Recently, however, the many drawbacks of using corn as a biofuel feedstock have become apparent. Any biofuel feedstock must not compete with food supplies in order to be considered a viable large scale alternative fuel. Biofuels that do not compete or interfere with food production are attractive because the end product is a fuel that is near identical to petroleum based fuels and will not require any substantial reworking of the current transportation fuel infrastructure. Vehicles based on electric power or fuel cells would require entirely new vehicle designs and significantly modified fuel or power distribution systems. When considering biofuel feedstocks for development it is also important to consider the water consumption and land area that will be required to produce the feedstock.
Microalgae have recently emerged as a promising biofuel feedstock because they meet many of the criteria stated above. The lipid portion of the microalgae biomass can be converted into a form of diesel which is nearly identical to petroleum diesel. In addition, production of algae does not interfere with world food production in any significant way.
Two general approaches are currently utilized for algae culture. Open systems (such as open ponds or raceways) are highly economical to build and operate; however, they have significant disadvantages, such as contamination risk, fluctuations in environmental conditions, and lower and less reliable productivity. Closed systems (such as photobioreactors) have the advantages of control of environmental conditions, low risk of contamination, and higher productivity and reliability than open systems. The primary disadvantage of closed systems is their relatively high cost for construction and operation.